Float pumps have been long used as a means for raising a liquid above the static surface level thereof. But the pumps of this type have commonly had a short stroke requiring considerable horsepower to effect the pumping operation. The present invention provides an apparatus and technique whereby the stroke can be lengthened and the horsepower requirement can be drastically reduced, and in fact reduced to a level at which the pump can be operated manually, even in raising the liquid from great depths below the static surface level thereof, and/or raising it to considerable heights thereabove. In particular, the pump can be operated by a person pedalling a pair of cranks with his legs, for example, in the manner in which a bicycle is pedalled.
When a float pump is put to use, the distal end portion of the same is inserted downward into the body of liquid until the intake of the tubular case of the same is immersed below the static surface level of the liquid. Meanwhile, the proximal end portion of the case is retained above the static surface level of the liquid, to discharge the pump effluent thereabove, and the piston rod of the pump is extended from the bore of the case to a point above the discharge, to enable the piston to be reciprocated therefrom, there being an annulus defined between the rod and the case in the bore thereof within which the liquid is lifted by the piston to the discharge of the case.
Since the piston is immersed in the body of liquid, it is subjected to hydrostatic forces. These may have a tendency to raise the piston out of the bottom of its stroke until its center of buoyancy and center of gravity reach a state of equilibrium. This tendency is a function, however, of the weight of the column of liquid in the annulus, the friction between the piston and the case, and the presence of any artesian forces acting on the piston. It is also a function of the buoyancy inherent in the piston itself, including the piston rod which is a part of the same, and the connection between the rod and the drive mechanism for reciprocating the piston.
The piston may also have a tendency to sink at the top of its stroke. This is a function of the weight of the piston, as well as any liquid which was not discharged from the annulus on the upstroke of the piston. The tendency is counteracted, of course, by the friction encountered by the piston, and by the resistance offered by the liquid captured between the piston and the intake of the case.
The tendency of the piston to rise can be referred to as "positive buoyancy" and the tendency to sink can be referred to as "negative buoyancy."